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Circumstellar Disks Around Rapidly Rotating Be-Type Stars, Yamina Touhami
Circumstellar Disks Around Rapidly Rotating Be-Type Stars, Yamina Touhami
Physics and Astronomy Dissertations
Be stars are rapidly rotating B-type stars that eject large amounts of material into a circumstellar disk. Evidence of the presence of a disk is found through hydrogen emission lines in their spectra, IR excess flux, and linear intrinsic polarization. In this dissertation, we report the first simultaneous interferometric and spectroscopic observations of circumstellar disks around 24 bright Be stars made using the techniques of long baseline interferometry and moderate resolution spectroscopy in the near infrared. The goal of the project is to characterize the fundamental geometrical and physical properties of the emitting regions that are responsible for the IR …
Sizing Up The Stars, Tabetha Suzanne Boyajian
Sizing Up The Stars, Tabetha Suzanne Boyajian
Physics and Astronomy Dissertations
For the main part of this dissertation, I have executed a survey of nearby, main sequence A, F, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars to better than 4% accuracy. The results of these observations also yield empirical determinations of stellar linear radii and effective temperatures for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale isochrones to constrain the masses and ages of the stars. These quantities are compared to the results found in Allende Prieto & Lambert (1999), Holmberg et al. (2007), and Takeda …
Dust Within The Central Regions Of Seyfert Galaxies, Rajesh Deo
Dust Within The Central Regions Of Seyfert Galaxies, Rajesh Deo
Physics and Astronomy Dissertations
We present a detailed study of mid-infrared spectroscopy and optical imaging of Seyfert galaxies with the goal of understanding the properties of astronomical dust around the central supermassive black hole and the accretion disk. Specifically, we have studied Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8-1.9s and 58 Seyfert 1s and 2s available in the Spitzer public archive, and the nuclear dust morphology in the central 500 pc of 91 narrow and broad-line Seyfert 1s using optical images from the Hubble Space Telescope. We have also developed visualization software to aid the understanding of the geometry of the central …
Electrical And Optical Characterization Of Group Iii-V Heterostructures With Emphasis On Terahertz Devices, Aruna Bandara Weerasekara
Electrical And Optical Characterization Of Group Iii-V Heterostructures With Emphasis On Terahertz Devices, Aruna Bandara Weerasekara
Physics and Astronomy Dissertations
Electrical and optical characterizations of heterostructures and thin films based on group III-V compound semiconductors are presented. Optical properties of GaMnN thin films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on GaN/Sapphire templates were investigated using IR reflection spectroscopy. Experimental reflection spectra were fitted using a non - linear fitting algorithm, and the high frequency dielectric constant (ε∞), optical phonon frequencies of E1(TO) and E1(LO), and their oscillator strengths (S) and broadening constants (Γ) were obtained for GaMnN thin films with different Mn fraction. The high frequency dielectric constant (ε∞) of InN thin films grown by the high pressure chemical …
A Prototype Visible To Near-Infrared Spectrograph For The Chara Array, A Long-Baseline Stellar Interferometer, Chad Elliott Ogden
A Prototype Visible To Near-Infrared Spectrograph For The Chara Array, A Long-Baseline Stellar Interferometer, Chad Elliott Ogden
Physics and Astronomy Dissertations
This work is a description of the Visible to near Infrared Spectrograph system for the CHARA array. The CHARA Array is a 6-telescope interferometer at the Mount Wilson Observatory in the mountains north of Pasadena, California. It combines the light from the 1-meter telescopes, and measures the visibility of the resulting interference fringes, which gives information about the source intensity distribution on the sky. The resolution of the instrument is proportional to the telescope separation, or baseline, divided by the wavelength. The VIS system operates in the 600-1000~nm wavelength range, a factor of 3 to 4 shorter than the standard …